Process of removing weakly acidic substances from oils



Patented Sept. 9, 1947 PROCESS OF-REMOVING WIiAKLY ACIDIG' SUBSTANCESFROM OILS Oheaterl. Adams, Hirhiand, and Theodore a. Tom, Hammond, Ind.,assignors to Standard Oil Company, Chicago, Iil.,- a corporation ofIndiana No Drawing.

This invention relates to the extraction of weakly acidic substancesfrom oils such as hydrocarbon oils and it relates more particularly tothe refining of petroleum products, naphtha, gasoline, kerosene, andsimilar oils containing small amounts of weakly acidic substances suchas mercaptans diflicult to remove by ordinary alkali washing.Heretoi'ore it has been proposed to facilitate the extraction of suchweak acids as mercaptans, phenols, etc., by extraction with causticalkali solutions containing mercaptan solubilizing agents calledsolutizersi' These solutizers are usually organic substances having ahigh. solubility in the caustic solution, while cha g ng the characterof the caustic solution in some way not Application December 7, 1944,Serial No. 567.114

11 Claims. (Cl. 196-80) 2 In the above formulas, R is alkyl,cycloalkyL-aryl or aryl-alkyl, R1 is an alkylene group having from oneto tour carbon atoms, and R: is an alkyl radical or hydrogen. Typicalsubstituted aminoacids we may use are dimethyl-, diethylanddipropylamlnoacetic acid, butylaminoacetic acid, dimethylaminobutyricacid and methylethylaminopro- .pionic acid. In general we prefer toemploysubstituted amino acids having from 3 to 8 carbon atoms. 7,

In the extraction of mercaptans from naphthas with a caustic soda orcaustic potash solution havllng a concentration of about 5 to 25 percent. we

- can employ about 5 to 35 per cent of substituted fully understood toincrease the solubility oi the weak acid in the caustic.

When employing solutizers, it is necessary to regenerate the causticsolution at'frequent inter.- vals to remove therefrom the weak acids, e,g.

amino acid solutizerin the form 01' its sodium or potassium salt.Expressed'in molarity, in most operations a tree caustic concentrationof about 2 to 5 is preferred. and such a-solutionwill preterably containabout 1 to 4 molar concentration me captans, and recycle the regeneratedcaustic or solutlzer. It'ls not necessar to employ pure substitutedamino acids'but mixtures 01" diflerent solution; otherwise the cost ofthe chemicals would be too great to be tolerated. Regeneration has beeneffected by'dlstillation, by oxidation, or by other means.

It is an object of our invention to facilitate the extraction ofmercaptans and other weak acids from oils by employin a more effectivesolutizer than those previously employed. Another object of ourinvention is to provide a solutizer for the extraction of mercaptansfrom naphthas, gasoline, etc. which is highly resistant to oxidationduring regeneration. Other objects of the invensubstituted amino acidsmaybe employed as well as mixtures of substituted amino acids with othersubstances having a solutizing action such as the phenols, the lowmolecular weight fatty acids, naphthenic acids, etc; The term-phenols"is used to denote the general class including the cresylic .acids,chlorinated phenols, cresols, etc., the xylenolsand others. In theextraction of naphthas, particularly cracked naphthas, it is commonlyfound that phenols are present in the tion will be observed from thefollowing description thereof:

According to our process, we employ as solutizers the N-substitutedamino acids having either one or both -NH2 hydrogens substituted withalkyl or other hydrocarbon radical. In general, the (ii-substitutedamino acids are preferred for their increased resistance to oxidation.The following type formulas illustrate the class or compounds which wemay employ as solutizers:

mo 0 on \NRL COOH R-N/ Ri alcoon' \NCEOO0H \N-CH-QOOH Ba Hr-C 0 OH R:

naphtha in suiilcient concentration to build up a considerableconcentration in the caustic'solution employed for extracting mercaptanstherefrom. The concentration of phenols obtained in this way can bereadily regulated, for example by pre-extraction oi a part of thephenols with caustic solution, with liquid ammonia, or other suitablesolvent for phenols. Excessive concentration of phenols collecting lnthecaustic solutizer solution may also be reduced from time to time bydiscarding a portion of the solution from which phenols may be sprungwith acid if desired and Bl nooc-ar-15-m-coon ass-mes from which thesolutizer may be recovered and returned to the system.

The unusual eflectiveness of the substituted amino acid solutizers isindicated by the results obtained on extraction of a painter's naphthasolution containing butyl mercaptan. The data set forth in the table'show the results obtained with dimethylamino acetic acid in comparisonwith amino acetic acid. The data also show the results obtained withmixtures of substituted amino acids with cresylic acid all in the formof their potassium or sodium salts employed in caustic potash or sodasolutions as indicated. I The procedure was as follows:

A naphtha solution of butyl mercaptan was prepared by adding suillcientbutyl mercaptan to painters naphtha to bring the copper number to 100.Five volumes of the resulting sour naphtha were stirred rapidly for tenminutes with one volume of the solutizer solution being tested. Anitrogen atmosphere was employed during the mixing operation to avoidoxidation of any mercaptan. The mixture was then allowed to settle forfive minutes, the naphtha layer was separated, washed twice with water,and the copper number was then determined. The copper number is a trueindication of the mercaptan concentration, the test being made in thefollowing manner: A 100 ml. sample of naphtha is titrated with standardammoniacal copper solution, 1 ml. of which is equivalent to 1 mg.mercaptan sulfur per 100 ml. (1 copper number). The end point isobserved when the blue color fails to be discharged after shaking.

, 4 for example by stripping with steam. the alkali mercaptides beingdissociated at elevated temperature, thus releasing the mercaptans fromthe caustic solution. We prefer, however, to eflect regeneration bycontacting the solution with air or oxygen at slightly elevatedtemperatures. for example 100 to 130 F. Under these conditions themercaptans are oxidized to the corresponding disulfldes which areinsoluble in caustic and which may be removed as a separate layer. Theseparation of the disulfldes can be facilitated by adding a suitablehydrocarbon solvent at this point in the system.

when employing the oxidation regeneration method, we may accelerate theoxidation by addition of various catalysts, preferably the polyphenolssuch as hydroquinone and catechol described in the patent of ErnestPevere, U. 8. 2,015,038 (September 1'1, 1935). We may also usepyrogallol, tannin, protocatechuic acid, gallic acid, and similarphenolic mercaptan oxidation catalysts. The amount of catalyst requiredfor the purpose is usually of the order of 0.1 to l per cent.

Having thus described our invention what we claim is:

1. The process of removing weakly acidic substances from oils whichcomprises extracting said oils with an aqueous solution of causticalkali and an alkali metal salt of an N-substituted amino acid in whichthe amino nitrogen is attached to at least one hydrocarbon radical.

2. The process of claim 1 wherein the concentration of caustic alkali isabout 5to 25 per cent Extraction of 100 copper number naptha ityPartitionC up a o- Oompositiou of Caustic Solution After emcientComments traction 6N KOH, 3N Dimethylaminoaoetate 6 78 Emulsiiied. Somesalting out took place- 4N KOH, 2N Dimethylaminoacetate, N Cr late 4 1203.6N KOH, 0.9N Dimethylaminoacetate, 1.8 Cresylate 1 495 Aboutentrainment. 3N NaOH, 0.9N Dimethylaminoacetate, 1.7N Cresylate 7. 5 62About a entrainment settled out rapidly. 5.5N KOH, 2.7N A 27 14 Haltedout at oono. 6-3. 4N KOH, 2N Aminoaoetate, N Cresylate 10 3.6N KOH, 0.9NAminoaeetate, 1.8N Cresylate..- 4 1% 3N NaOH, 0.9N Aminoacetate, 1.7NCresylate 7. 5 62 Emulsifled badly. 2% entrainment.

l Emulsion broken with small amount of Tretolite L-l6508.

i The once-used solutlzer solution was used again: copper No. 100

" Emulsion broken with diflleulty using Tretolite 11-15508.

It will be noted from the foregoing data that in a practically all casesthe extraction of mercaptans is more complete when employing thedlmethylaminoacetic acid solutizer than when employing the unsubstitutedamino acetic acid at the same concentration. Furthermore, the use of theunsubstituted amlno acetic acid has a tendency to develop emulsionswhich are very troublesome, especially in large-scale commercialoperations.

In carrying out our process of mercaptan extraction on a commercialscale, we prefer to extract the naptha countercurrently either in aseries of mixers and settlers or in an extraction tower provided withsuitable packing or baiiles to insure eflicient countercurrentcontacting. The extracted naptha is discharged at the top of the towerwhile the caustic solution is withdrawn at the bottom and conducted tothe regeneration step. The dissolved mercaptans may be discharged fromthe caustic solution by distillation,

and the concentration of substituted 0 acid is about 5 to 35 per cent.

3. The process of removing weakly acidic substances from oils whichcomprises extracting said oils with an aqueous solution of a causticalkali and an alkali metal salt of a dialkyl amino acid, having bothalkyl groups substituted on the amino nitrogen.

4. In the process of extracting mercaptans from a petroleum distillatewhich comprises 'coiuitercurrently contacting said distillate with anaqueous caustic alkali'solution containing a solutizer in sufilcientconcentration to substantially increase the solubility of saidmercaptans in said caustic solution, separating the caustic solutionfrom the distillate, subjecting it to regeneration by removing dissolvedmercaptans therefrom and recycling said caustic solution containing saidsolutizer to-the contacting step for the extraction of furtherquantities of distillate, the improvement comprising employing as saidsolutizer an N-substituted amino acid in which the amino nitrogen isattached to at least one hydrocarbon radical.

5. The process of claim 4 wherein said regeneration is effected byoxidizing dissolved mercaptans in said caustic solution to disulfldes bythe action of oxygen and separating the resulting disulfldes from thecaustic solution.

6. In the process of sweetening' sour petroleum distillates containingmercaptans which comprises extracting one such distillate with anaqueous caustic alkali solution having a concentration solutioncontaining sufllclent diethylaminoacetic acid to increase substantiallythe solubility of said weakly acidic substance in said caustic solution.10. The process of removing a weakly acidic substance from hydrocarbonoils which comprises extracting said oils with a strong aqueous causticsolution containing suflicient dimethylaminobutyric acid to increasesubstantially the solubility of said weakly acidic substance in saidcaustic of about 2 to 5 normal free caustic and a solutizer 10 solution.

serving the purpose of increasing the solubility of mercapta'ns in saidcaustic solution, separating said caustic solution from said distillate,regenerating said caustic solution by removing therefrom dissolvedmercaptans and recycling the regenerated caustic solution to theextraction step for treatment of further quantities of distillate, theimprovement comprising using as said solutizer an N-substituted aminoacid in a concentration of about 1 to 4 molar, said N-substituted aminoacid having at least one hydrocarbon radical attached to the aminonitrogen atom.

7. The process of claim 6 wherein said caustic solution is regeneratedby contacting with air in the presence of a small amount of a polyphenolmercaptan oxidation catalyst, thereby converting said mercaptans todisulfldes which are insoluble in said caustic solution and thereafterremoving the said disulfldes from the caustic solution before recyclingto said contacting step.

8. The process of removing a weakly acidic substance from hydrocarbonoil which comprises extracting said oil with a strong aqueous causticsolution containing suflicient dimethylaminoacetic acid to increasesubstantially the solubility of said weakly acidic substance in saidcaustic solution.

9. The process of removing a weakly acidic substance from hydrocarbonoils which comprises extracting said oils with a strong aqueous caustic11. The process of removing'mercaptans from petroleum distillates whichcomprises extracting said distillates with an aqueous solution of acaustic alkali containing a solutizer in suflicient,

concentration to increase substantially the solubility of saidmercaptans in said solution, said solutizerconsisting essentially of amixture of alkali metal salts of cresylic acid and an N-substitutedamino acid, in which the amino nitrogen is attached to at least onehydrocarbon radical. CHESTER E. ADAMS. THEODORE B. TOM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS.

